Summary of Work: The purpose of this project is to examine risk factors leading to the epigenesis of stuttering and cluttering. Speech planning and production were examined in an experimental study of speech processing in adults with chronic stuttering and control subjects. A model of parallel and serial speech processing during ongoing speech was developed. This model predicted that when individuals who stutter are disrupted during ongoing speech, they will be slower to restart the same utterance due to serial processing, rather than switching to a new utterance involving simultaneous parallel processing. Thus tasks requiring parallel and serial planning of a new utterance were compared during a simple speech execution task which did not involve planning. These tasks also examined the role of speech material. Performance using material containing familiar, meaningful words was compared with that using nonsense syllable production. The facility of adults who were chronically affected with developmental stuttering and control subjects on the planning and production tasks was compared. First, the role of parallel processing in speech planning was demonstrated as both groups were able to restart interrupted speech more quickly when parallel processing was possible than when serial processing was required. Second, the increased processing demands when meaningful speech was employed ware demonstrated as the speech of both groups was more fluent when nonsense syllables were produced. In addition, the individuals who stuttered were less efficient than the control subjects on all items requiring speech planning, but efficiency was comparable on the speech production items. Finally, the difference between individuals who stuttered and control subjects was greater when meaningful words were produced than with nonsense syllables with the same production requirements. The results suggest that stuttering involves a disorder of speech planning rather than a motor execution disorder and that speech processing at the linguistic level is affected rather than motor execution. This project will be terminated.